Several materials and compounds have been discovered to be superconducting. Superconductors have been proposed to serve in a variety of applications. These applications include motor windings, superconducting cables, test coils, actuators, magnetostrictor coils and vapor-cooled leads. However, many of these superconducting materials which apparently carry current with electron holes or in some cases with electrons are extremely difficult to work into useful configurations. Superconductors are generally formed of relatively brittle materials such as ceramic, ceramic-metal compounds (cermets) and metal oxides which are inherently difficult to form into practical and useful shapes.
A quick survey of the recent technical literature through Chemical Abstracts has indicated that the following oxide materials including compounds, phases, mixtures, doped materials, etc. have been proposed for superconducting use:
YBa.sub.2 Cu.sub.3 O.sub.7-x PA0 MBa.sub.2 Cu.sub.3 O.sub.7 M=Nd, Dy, Er, Tm or mixtures PA0 MBa.sub.2 Cu.sub.3 O.sub.6 M=Sa, Ho PA0 La.sub.2-x Sn.sub.x CuO.sub.4 PA0 La.sub.2 CuO.sub.4 doped with fluorine PA0 YBa.sub.2 Cu.sub.3 O.sub.6.8 doped with fluorine PA0 EuBa.sub.2 Cu.sub.3 O.sub.9-x PA0 EuBa.sub.2 (Cu.sub.1-y M.sub.y).sub.3 O.sub.9-x M=Cr, Mn, Fe, Co, Ni or Zn PA0 GdBaCu.sub.3 O.sub.7-x PA0 Ba.sub.2 SmCu.sub.3 O.sub.9-x PA0 InSnO.sub.2 PA0 La.sub.2-x M.sub.x CuO.sub.4 PA0 La.sub.2-x Sr.sub.x CuO.sub.4 PA0 Ba.sub.2 YCu.sub.3 O.sub.9-y PA0 GdBa.sub.2 Cu.sub.3 O.sub.7-x PA0 YBa.sub.2 (Cu.sub.1-x Fe.sub.x).sub.3 O.sub.7-y PA0 (Y.sub.1.2 Ba.sub.0.8).sub.4 Cu.sub.4 O.sub.16-x PA0 YBa.sub.3 Cu.sub.3 O.sub.y F.sub.x PA0 Y.sub.3-x Ba.sub.x Cu.sub.2 O.sub.7-y PA0 Bi--Sr--Cu--O system PA0 La.sub.3-x Ba.sub.3-x Cu.sub.6 O.sub.14-y PA0 YBa.sub.2 Cu.sub.3 O.sub.7-x S.sub.y PA0 EuBa.sub.2 Cu.sub.3 O.sub.x PA0 YBa.sub.2 Cu.sub.3 O.sub.9-y PA0 La.sub.1.85 Sr.sub.0.15 CuO.sub.4 PA0 Ba.sub.2 RCu.sub.3 O.sub.x R=Gd, Ho, Er or Dy PA0 YBa.sub.2 (Cu.sub.1-x Ag.sub.x).sub.3 O.sub.7-y PA0 YBa.sub.2 (CuO.sub.0.94 FeO.sub.0.06).sub.3 O.sub.9-y PA0 YBa.sub.2 Ag.sub.3 O.sub.x PA0 La.sub.2 CuO.sub.4-y PA0 Dy.sub.x Ba.sub.1-x CuO.sub.3-y PA0 Molybdenum Oxides and Bronzes-Alkali Molybdenum Bronze PA0 Nb, Si, Al oxides Japanese Pat. Appln. No. 87-170,108 PA0 Ge, Al, Nb oxides Japanese Pat. Appln. No. 87-171,924 PA0 BaPb.sub.1-x Bi.sub.x O.sub.3 PA0 Nb/Al--Al.sub.2 O.sub.3 PA0 Nb/Ge--Al--O PA0 Pb, Bi, In oxides PA0 Li.sub.1-x Ti.sub.2-x O.sub.4 ##EQU1##
Proposed methods of forming superconductors include grinding oxide into ultrafine particles and extruding the ultrafine particles and applying a binder to superconducting materials or precursors to hold material together during a forming process. The problems with the ultrafine particles include cost of reducing the size of the particles, low strength and excessive number of grain boundaries which limit superconductivity. The problems with using binders include the contamination remaining from binders which are not completely removed during sintering, low strength and complex processing techniques.
An alternative and successful method of preparing superconductor materials comprises producing by energetic milling of metallic powder a precursor alloy and oxidizing the precursor alloy into a superconducting material. A method of oxidizing the precursor is described in U.S. Pat. No. 4,826,808 ('808). Formed precursor alloys have been successfully heat treated according to the oxidizing procedure of the '808 patent to produce superconducting wire. However, difficulties have arisen in the steps of energetic milling metal powder to produce oxide superconductor precursor alloy and forming of the precursor alloy. The difficulty entails the in situ difficult to work, brittle intermetallics phases. During high energy milling of silver with elemental components of an oxide superconductor, a variety of intermetallics may be formed. For example, high energy milling Ag, Ba, Cu and Y powders together, intermetallics formed have included Ag.sub.5 Ba, Cu.sub.5 Ba, AgY, Ag.sub.6 Y, CuY, Cu.sub.4 Y.sub.2, Cu.sub.4 Y and Cu.sub.6 Y. These intermetallics impair ductility and increase difficulty in working or forming the precursor alloy into a desired shape.
It is an object of this invention to provide a method of producing metallic, superconductor precursors which limits the amount of ductility decrease from the formation of non-ductile compounds or phases.
It is a further object of this invention to provide a method of mechanical forming of non-ductile superconductor precursors.
It is a more particular object of this invention to provide a method of forming 1-2-3 Y-Ba-Cu precursor into useful shapes such as wires.